Can forces be combined?
Yes, they can.
Forces can be described mathematically by vectors, which can be added or subtracted depending on their directions.This link gives helpful insight .
Forces acting in the same direction can have their magnitudes added to each other to create the resultant force.
Forces acting in opposite direction can have their magnitudes subtracted to create the resultant force.
Forces acting perpendicularly to each other can be placed "head to tail" to create a right-angled triangle and then the resultant magnitude can be said to be the hypotenuse of the triangle, which is found using Pythagoras's theorem.
Forces acting at an angle can be split into horizontal and vertical components using Trigonometry which can then be combined with other forces (if needed)